1. Field of the Invention
The present invention relates to a recording medium, a recording method, a recording apparatus, a reproducing method, and a reproducing apparatus that are applicable to recording of address information in a recordable optical disk and reproduction of the address information.
2. Description of the Related Art
Various formats have been proposed for optical disks. As recordable optical disks, there are a write-once optical disk in which it is possible to record data only once and a rewritable optical disk in which it is possible to rewrite data. In both the kinds of optical disks, addresses indicating positions in a recordable track provided on the disk need to be recorded in advance. As a method of recording the addresses and clock information, a method of forming a wobble groove on a disk has been proposed.
In an address format (see JP-A-2003-123249 and JP-A-2003-123267) adopted in a latest rewritable high-density optical disk (Blu-ray Disc (registered trademark), both MSK and STW (Saw Tooth Wobble or HMW grooves, i.e., High Frequency Modulated grooves) are used.
As shown in FIG. 13, a group of fifty-six wobbles in total is set as an ADIP unit. One bit of “0” or “1” synchronization information, a reference unit, or a monotone unit is represented by this ADIP unit. Eight kinds of ADIP Units (a monotone unit, a reference unit, four kinds of synchronization units, and two kinds of data units representing data “0” and “1”, respectively) are shown in FIG. 13. Eighty-three continuous ADIP Units form an ADIP word indicating one address. The ADIP word includes address information having a 24-bit length, auxiliary data having a 12-bit length, a reference area, and data for error correction. Three ADIP words are allocated to one RUB (Recording Unit Block) (in a unit of 64 kilobytes), which is a unit for recording main data.
As shown in FIG. 13, wobble numbers 0 to 55 are added to the ADIP units including fifty-six wobbles to distinguish the ADIP units. For example, sections from the wobble numbers 0 to 2 are modulated by the MSK and sections from the wobble numbers 18 to 54 of the reference unit and the data unit are modulated by the STW. The monotone wobbles not modulated by the MSK and the STW are a waveform (cos(2π ft)) of a predetermined frequency.
The STW system is a system for generating a modulation waveform similar to the teeth of a saw by adding a second harmonic (sin(2π2 ft)) to a basic wave (cos(2π ft)) or subtracting the second harmonic (sin(2π2 ft)) from the basic wave (cos(2π ft)). An amplitude of the second harmonic is set to be as small as about ¼ of the basic waveform. Since one of the addition and the subtraction is selected according to “0” or “1”, the modulation waveform is varied. Data is repeatedly recorded in the sections of the wobble numbers 18 to 54 of the reference unit and the data unit.
The two kinds of systems are used as described above in order to make it possible to compensate for disadvantages of the respective systems. In the MSK system, one bit is recorded by modulating first three wobbles of an ADIP unit. Thus, it is possible to use the wobbles as a reference for determining a position of data at the time of reproduction. On the other hand, in the STW system, data is repeatedly recorded over a wide range as a very small waveform change. At the time of reproduction, a reproduced signal is integrated to discriminate “0” or “1”. Therefore, it is difficult to use the reproduced signal as information for detecting delimiters of data. However, the MSK system, which is a local recording system, is easily affected by a defect due to scratches, dust, and the like on a disk. The STW system has an advantage that the system is less easily affected by such a defect because data is recorded over a longer period.